Inorganic cation-capped SnO₂ for high-performance perovskite solar cells

A thin SnO₂ electron transport layer (ETL) of thickness ∼30 nm is commonly utilized in the fabrication of high-efficiency perovskite solar cells (PSCs) with a regular structure. A fine yet uniform nanoscale surface modification layer, on such a delicate SnO₂ layer, can significantly optimize the energy levels, reduce backward carrier recombination, and mitigate strain within the perovskite layer. This study demonstrates that La capping, deposited on the SnO₂ surface via chemical bath deposition (CBD), induces a conduction band spike at the interface and mitigates strain in the perovskite layer. This approach suppressed the formation of an undesired δ-phase of the formamidinium lead triiodide (FAPbI₃) at the buried interface, enhanced electron transport, and significantly improved the performance of the resulting device. The champion device, fabricated with La-capped SnO₂ as the ETL, achieved a power conversion efficiency of 26.2% (with a certified efficiency of 25.6%) and demonstrated excellent operational stability, retaining over 80% of its initial efficiency under continuous light illumination for 800 h.